1. Field of the Invention
The invention is directed to a spring strut, especially for motor vehicles, comprising a hydropneumatic vibration damper and a supporting spring.
2. Description of the Related Art
A prior art spring strut is disclosed, for example, from DE 44 03 196 A1, wherein the vibration damper has a characteristic diagram of damping force suited to requirements. This is achieved in that the damping force characteristic diagram is formed of at least three individual force diagrams. A first damping force characteristic diagram takes effect within a middle range associated with the relatively short springing-in movement. The first damping force characteristic diagram exerts a small, preferably decreasing, damping force in response to these small spring paths. In this way, unevenness in roadways such as cobblestones which act on the vibration dampers at higher frequencies are damped to a lesser degree.
This first damping force diagram passes into another damping force diagram with rising damping values both in the pull direction and in the push direction, so that larger springing-in and springing-out movements are progressively damped. This is achieved by a damping valve arrangement in the region of the piston rod guide with a flow direction for the pull direction and push direction. The damping valve comprises a valve spring upon which the spring force of the vehicle supporting spring is superposed in an additive manner. A load-dependent action of the vibration damper is achieved in this way. A pressure buffer which takes effect during a larger springing-in movement generates an increase in damping force, while a hydraulic-mechanical tension stop takes effect during larger springing-out movement. A disadvantage in this construction consists in that the load-dependent action of the vibration damper in particular is directly dependent on the springing force of the supporting spring, so that a predetermined desired damping force process is not realizable.